[Amps] AL-1500 Circuit Diagram

[TexasRF@aol.com]

In a message dated 3/1/2005 10:49:36 A.M. Central Standard Time,  r at somis.org 
writes:

In the  AL-1500 diagram, the cathode is connected to one side of the 
heater,   C7 couples RF from the tuned-input to the cathode ,and C8 
couples RF from  the tuned-input to the other side of the heater.  Can 
someone please  explain why the heater is driven with RF?

Richard L. Measures, AG6K,  805.386.3734.  www.somis.org  

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The most likely reason is to limit the voltage between the heater and  
cathode. If the filament was not tied to the cathode there could be rf voltage  on 
the order of 90v peak or more between the cathode and filament. I didn't see  a 
specification for this in the old data sheet I have here. A breakdown test  
could give a hint here.
 
Also, if the cathode became open circuited for some bizarre reason, like  the 
series cutoff bias resistor opened up, the cathode voltage could rise to  
near the plate voltage. This would not be good for the cathode to filament  or 
cathode to grid interface.
 
Was this a trick question?
 
73, K5GW